I was using a DSLR x1.6 sensor + Canon EF 24-105mm L IS lens. Conditions are never as you would like them. I was shooting through the perspex windows of Polly's Cherokee from the backseat, to allow shots from both sides of the aircraft. We were flying straight to Wickenby after joining up with the BBMF pair a few miles from Coningsby. As it was evening and the route roughly due north, the sun was constantly on the Spitfire on our starboard wing. If we had been able to make a few turns then things could have been more interesting, but as the escorting fighters had more important things to do, this was not possible. Prop' blur is important, to convey movement. So on looking up the Spitfire's rpm at cruising speed, I was able to calculate the ideal shutter speed for my camera. 1200 rpm x 4 propeller blades divided by 60 suggests a shutter speed of 1/80th second for a full 360 degree propeller blur. The problem now was could I keep the camera still and would the aircraft alongside us be steady enough in the bumpy conditions, to get a sharp image? The answer could only really be found out after reviewing the shots at the end of the photo shoot. I could not afford to take chances, so I decided to use a whole range of shutter speeds from 1/80th to 1/250th for insurance purposes. Afterwards I found I had blurred shots at all speeds, but most of the better shots were at 1/125th, which seemed at the time the best shutter speed to use. In the 6½ minute flight in formation I actually took 150 shots.